Preheat oven to 180 degrees celsius (fan-forced).
Grease and line a 20cm square baking tin with baking paper and set aside.
Place the butter, brown sugar and golden syrup into the Thermomix bowl. Melt for 3 minutes, 80 degrees, Speed 2.
Add the self-raising flour, chopped dates, lemon zest and salt and mix on Reverse, Speed 4, 5 seconds. Scrape down the sides of the bowl and repeat for a further 5 seconds or until combined.
Pour the mixture into the prepared baking tin and cook for 15 minutes or until lightly golden and cooked through.Allow the slice to cool completely in the tin before cutting into pieces.
Store in an airtight container at room temperature for up to 1 week.